Fine titanium oxide powder in various forms such as granular, acicular, dendritic, flaky and other forms, has been so far known except for the hollow forms.
The fine hollow powder according to the present invention can be obtained by spray drying a laminated titania sol, as will be described later.
So far known processes for producing the laminated titania sol include a process, which comprises mixing cesium oxide or a compound decomposable to cesium oxide by heating with titanium oxide, followed by heating, treating the resulting layered cesium titanate with an aqueous acid solution, thereby replacing the interlayer cesium ions with protons (whose existing forms are hydronium ions), and mixing the resulting titanic acid powder with an aqueous solution of ammonium compound or amine compound under stirring (JP-A-9-25123). However, the process suffers from a low reactivity of the cesium titanate with the aqueous acid solution and a long time, for example, at least 3 days, in the replacement of the cesium ions with the protons (whose existing forms are hydronium ions) (JP-A-6-122518), and is very inefficient and costly in the commercial production.
Layered alkali metal titanate compounds with parts of host framework Ti4+ sites being vacant or replaced with divalent or trivalent alkaline earth metal ions or transition metal ions, such as said cesium titanate [for example, as disclosed in I. E. Grey, I. C. Madsen and J. A. Watts, J. Solid State Chem. 66, 7 (1987), D. Groult, C. Mercey and B. Raveau, J. Solid State Chem. 32, 289 (1980), etc.] can only serve to exchange their interlayer ions, with the result of an insufficient ion exchangeability and inefficient production of exfoliated titania sol.
The well known process for producing thin flaky titanium oxide particles comprises freeze drying an exfoliated titania sol (JP-A-9-67124). However, the process requires freeze drying of a dilute exfoliated titania sol to obtain fine powder with a distinguished dispersibility. That is, freezing of a relatively large amount of water is inevitable before vacuum drying and thus an enormous amount of energy must be consumed, causing an economical problem.